DC-DC power conversion at low- to medium-power levels is possible using several classical and new topologies that employ MOSFETs or BJTs for active current switching. These topologies have very high frequencies for advantageously reducing reactive element sizes. However, these converters do not scale up efficiently when the power requirements extend to the hundreds of kW or MW range.
Resonant converters which use a capacitor and inductor in series to provide DC-DC conversion suitable for high-power applications are advantageous because of their natural commutation and soft switching ability. Examples of such converters include the series resonant converter (SRC) (see F. C. Schwarz & J. B. Klassen, "A Controllable 45-kW Current Source for DC Machines," IEEE Trans. on Ind. Appl., Vol. IA-15, No. 4, pp. 437-444, Jul./Aug. 1979), all quasi-resonant converters (see K. H. Liu & F. C. Lee, "Zero Voltage Switching Technique in DC/DC Converters," IEEE-PESC records, pp. 58-70, 1986), as well as the pseudo-resonant full-bridge converter (see D. M. Divan & O. Patterson, "A Pseudo-Resonant Full Bridge DC/DC Converter," IEEE-PESC Records, pp. 424-430, 1987).
Resonant converters, however, suffer from significant limitations in high-power applications. First of all, resonant converters require careful matching of the operating frequency at the resonant tank components. Secondly, any magnetic saturation or other unexpected drift in resonant frequency can result in operating failure. Moreover, during the resonant converter's operation, its input and output capacitor filters must handle large ripple currents and significant voltage and current stresses. Furthermore, using resonant converters it is not possible to step up or step down voltage without a transformer.
Thus, there is a need for a DC-DC converter circuit that does not require careful matching of operating frequency to components within the converter.
There is a need for a DC-DC converter that does not experience operational failure as a result of magnetic saturation or unexpected drift.
Other demands that the above DC-DC converters cannot begin to satisfy are the smaller size and lower weight requirements that are applicable to many high-power aerospace applications. To achieve high-power conversion in small, light-weight components, it is necessary to reduce transformer size and LC filter components. Primarily, this requires operation at high switching frequencies and reduction in device switching losses by applying soft-switching techniques.
Therefore, there is a need for a DC-DC converter circuit having smaller size and lower weight than known systems for high-power applications, including aerospace applications.
There is a need for a DC-DC converter circuit having a smaller transformer size and smaller LC filter components.
Moreover, there is a need for a DC-DC converter circuit capable of operating at higher switching frequencies with reduced switching losses.